Spreader for treating soil

ABSTRACT

A spreader for spreading treatment products on soil to improve the quality thereof is disclosed. The spreader consists of a vehicle including a frame (103) slidably housing an assembly (105, 106) of a hopper and a metering device. The frame also supports soil shearing means (114) located ahead of the hopper, and mixing means (112) located behind the hopper for mixing together the spread product and the loosened soil. As a result, soil treatment may be enhanced and the nuisance caused by spreading may be diminished.

This invention relates to spreaders which enable soil to be treated,more particularly by spreading onto it products intended to improve itscharacteristics, notably its mechanical characteristics, in order, inparticular, to allow other work to be carried out on top of it.

It is known that in order to construct a road or a car park, forexample, it is very uncommon to be able to lay down the necessarymaterials directly onto the rough ground. Apart from the laying out andgrading operations, it is often necessary to treat the soil by spreadingonto it a product such as lime or cement and then mixing these materialswith the original material of the soil. These soil treatment techniqueshave largely been developed in recent years. They have brought animportant development to prominence, in particular in temperate, humidareas, because they enable the moisture content of soils to becorrected, for example by supplying quicklime. Furthermore, and possiblyin addition to this additive, in areas where aggregates are rare it ismore economical to add cement, which allows a foundation layer to beproduced straight away.

Currently known materials for carrying out this type of treatment aredescribed in particular in European patent application No. 0462899, aswell as in French standard NFP98-712. By way of example, a knownspreader comprises a tank which acts as a silo, extraction meansenabling a hopper situated at the end of this tank to be supplied, and ametering device receiving the product from the hopper and spreading iton the soil. This assembly is integral with a supporting chassis whichcan be either towed or self-propelled. Rubber skirts placed around thematerial outlet opening allow wind effects to be limited to a greater orlesser extent.

Despite numerous attempts to improve these devices, of which theafore-mentioned French standard gives a fair summary, these machineshave undergone limited development. Consequently, and in spite of theseimprovements, the spreading technique has a long way to go beforeachieving a satisfactory level of development, and the defectsconcerning in particular the non-uniformity of longitudinal andtransverse dispersion are always present at a level which is frequentlydissuasive.

Because of the change in attitudes, one drawback which is becomingincreasingly important concerns the dispersal of dusts, which adverselyaffect the protection of the environment and the well-being of personsworking on the site or living in the vicinity. This drawback is nowconsidered so important that it frequently causes site work to stop, forexample in the presence of wind, which carries the dust over fairlylarge distances. This dust dispersal occurs when the spreader is filledby pulsed air transfer. Moreover, during spreading, in spite of thebasic protection afforded by the above-mentioned skirts, the powderyspread product often drops from an appreciable height--necessitated bythe need for an adequate clearance between the outlet of this productand the ground due to irregularities in this ground. The kinetic energyaccumulated during this fall by the particles is dissipated byrebounding on contact with the ground, causing a cloud of dust.

Furthermore, the mass of the product contained in the spreader hasirregularities in the density, which can be large, in particular whenthe spreader is loaded by pulsed air transfer. The product thus containsirregularly occluded air and its grains are furthermore charged withstatic electricity, which increases the irregularities in the density.This effect is even more marked when the product is delivered warm,which is also frequently the case.

Moreover, the product is extracted from the silo where it is containedby mechanical processes, such as a screw or a conveyor belt, to betransported to the metering device and distributor which in the majorityof cases are situated at the rear of the spreader. This causes anadditional change in the density of the product by compression and/orbulking. In certain cases extraction is effected by pulsed air and thedifferences in pressure which are produced inevitably have the sameresults on the density of the product. Furthermore, the producttransported in this way to the rear of the spreader is then generallydistributed transversely by means of divergent pitch screws, thenmetered for example with the aid of an alveolar drum, a helmet or aconveyor belt. This last operation further increases the risks ofirregularities in the distribution of the product on the surface of thesoil.

To overcome these drawbacks the invention proposes a spreader fortreating soil, of the type containing a silo and metering means placedat the lower part of the silo to be directly gravity fed from this silo,principally characterised in that the lower part of the silo forms ahopper having the form of a truncated prism whose base is upwards andwhose truncated lower part is directly attached to the metering deviceand extends, along with the metering device, over more or less theentire width of the spreader to treat the soil over more or less thisentire width without pulverizing the product to be spread.

According to another feature, the spreader contains supporting means tovertically raise and lower the silo/metering device assembly in order toadjust the distance between the soil to be treated and the meteringdevice.

According to another feature, these supporting means of thesilo/metering device assembly also enable said silo/metering deviceassembly to be tilted forwards and backwards.

According to another feature, these supporting means are formed from 3or 4 jacks situated at the periphery of the silo and articulated bymeans of trunnions or universal joints.

According to another feature, the metering device is a large diameterrotor type fitted with small cells.

According to another feature, the spreader contains means for attachingthe metering device to the hopper, enabling the type of metering deviceto be changed.

According to another feature, the spreader contains a frame which isopen over the entire width of the spreader to receive the silo, whosetransverse cross-section is constant with respect to the axis of thespreader and maximum with respect to the opening of the frame.

According to another feature, the spreader contains four wheels able topivot through 180 degrees, situated at the four corners of the frame, towiden the track, to increase the stability of the spreader, and to avoidcrushing the edges of the strip of material discharged onto the soil.

According to another feature, the spreader furthermore contains avertical transverse and central partition dividing the silo into twoparts, and means for controlled closing of the junction between thehopper and the metering device so as to feed the metering device via oneand/or the other of the two parts of the silo.

According to another feature, the spreader contains two rotatingmetering devices of different diameters intended to be fed by each ofthe two parts of the silo, respectively, and the vertical centralpartition is movable in order to delimit two unequal parts whose volumescorrespond to the flow rates of the metering devices.

According to another feature, the silo contains an opening able to beconnected to a filter enabling the air carried into the silo by themeans for filling this silo with the treatment product to be evacuated,before the start of work; this filter being supported by a trailer ableto be coupled to the spreader in a towing position or in atransportation position.

According to another feature, the spreader furthermore contains mixingmeans situated behind the metering device to provide mixing of the soiland the product spread on the soil at the front of the mixing means;these mixing means being attached to the frame by means for adjustingtheir height with respect to the soil.

According to another feature, the spreader furthermore contains twocasings enclosing the mixing means and the metering device,respectively, and containing openings fitting together one within theother in the operating position to provide sealing of the assembly.

According to another feature, the mixing means are divided into twoseparate parts with respect to the longitudinal plane of symmetry,separated and situated in front of each of the rear wheels,respectively, making a non-mixed space between them, to mix two stripsof soil intended then to be crushed by these wheels.

According to another feature, the spreader furthermore contains soilshearing means situated in front of the metering device to loosen thesoil prior to the spreading of the product; these shearing means beingattached to the frame by means for adjusting their height with respectto the soil, being able to operate independently of the other means foradjusting the heights of the silo and of the mixing means.

According to another feature, these shearing means are fitted with amotor enabling the tensile stress of the spreader on the shearing meansto be minimized.

According to another feature, the spreader furthermore contains meansfor measuring the weight of the silo/metering device assembly and meansfor processing the signals obtained by these measuring means, in orderto determine from the variation in this weight the flow of the productspread on the soil and to control the flow rate of the metering devicein order to obtain a uniform distribution of the product on the soil.

According to another feature, these measuring means operate on the oilpressure in the jacks, enabling the position of the silo to be adjusted.

According to another feature, the spreader furthermore contains meansenabling the position of the strip of product spread on the soil to bedetected and the direction of advance of the spreader to be controlledto maintain the successive strips of spread product contiguous with eachother.

Other distinctive features and advantages of the invention will beclearly revealed in the following description, given by way of anon-limiting example with reference to the accompanying figures, inwhich:

FIGS. 1 and 2 show side views of a spreader according to the invention,in the transportation position and in the operating position;

FIGS. 3 to 5 show side views of a variant of this spreader in one restposition and two operating positions;

FIG. 6 shows a side view of a variant of this spreader, containing adual metering device;

FIG. 7 shows a rear view of a filter adaptable to the spreaders of thepreceding figures;

FIGS. 8 and 9 show side views of this filter coupled to one of thesespreaders;

FIGS. 10 and 11 show side views of a spreader represented in FIGS. 1 and2, containing addition soil mixing means; and

FIGS. 12 to 14 show side views of a variant of a spreader represented inFIGS. 10 and 11.

The spreader according to the invention and shown in FIGS. 1 and 2 hasthe form of a self-propelled motor vehicle containing a chassis 103forming a completely open frame on which are mounted treatment deviceswhich will be described later. This chassis 103 rests upon at least foursingle or twin wheels 104 attached to the four corners of the chassis,respectively, by means of a support able to pivot about a vertical axis,which enables the stability of the spreader to be increased. By usingthe same steering radius for the front and rear wheels, the spacing ofthese wheels and the position of their vertical pivot enables theimprint of the wheels, as well as the throw of the product onto thesoil, to be arcs of circles admitting the same centre, and each wheel isat a tangent to the treatment section or crushes it at a distance suchthat its passing does not produce a widening of this section bycollapsing or crushing it. The quality of the work is thus improved.Furthermore, to limit the overall width of the assembly, the lateralstruts of the frame 103 are manufactured with a beam of small width, butsufficiently high to have the necessary strength.

At the front the chassis supports a cab 101 for the driver, and at therear the driving gear 102 enabling the necessary power for moving themachinery and for the operation of the spreading and soil treatmentdevices to be supplied, for example by hydraulic means.

The assembly designed to contain the treatment product and to spread iton the soil is formed by a silo 105, having the form of a more or lessparallelepiped tank surmounting a hopper in the form of a truncatedprism, terminated by a rotary metering device 106. The wide base of theprism faces upwards and its apex faces downwards. This apex is truncatedhorizontally at the bottom of the hopper to form a mounting joint 108between this hopper and the metering device 106, which is detachable.Under these conditions, the lateral parts of the silo are vertical withrespect to the axis of the vehicle, and the transverse parts areslightly inclined inwards in the high part, then inclined towards themetering device to form the hopper so as to directly feed this meteringdevice by simple gravity.

The walls of the silo are thus inclined so that the flow is smooth.Furthermore, the flow being gravitational, it is not necessary tofluidize the product, which eliminates all the problems caused byfluidization, as is necessary in known devices.

The metering device 106 extends the entire width of the silo and of thevehicle, the work is carried out at the full width and the spreadingwidth corresponds to more than the storage width, which means that thereis no additional handling of the product in order to adapt theextraction width in the silo to the spreading width, which eliminatesthe drawbacks resulting from this handling.

Moreover, such an arrangement allows large-scale systems to be used forthe metering device 106, such as for example the large diameter alveolardrum shown in the figure, or in variants a conveyor belt meteringdevice. The bolted attachment of this metering device to the joint atthe base of the hopper allows the metering device to be changed for bestadaptation to the work in hand. The use of metering devices of largedimensions also allows limited pulverization of the material to bespread, which reduces the movements inside the spreader and allowstrajectories of the product grains to be obtained which are coplanarwith a longitudinal plane. Since the trajectories are short, the speedsare reduced.

The result of all these arrangements is that the product is deaeratedduring its movement and its density is stabilized, which enables theconsistency of the spreading operation to be much improved.

Furthermore, for a given flow rate, the use of a large diameter drumallows the dimensions of the cells to be reduced, which allows betterdistribution of the product on the soil. It also enables a larger dailylinear flow rate to be obtained, which allows the efficiency of thespreader to be increased.

According to the invention, in order to attach the silo 105 to the frame103, adjustable means permitting the height of the assembly 105/106 tobe varied with respect to the ground will be used. For example, thesemeans will take the form of 4 jacks 107 placed at the four corners ofthe silo, as shown in the figure, or possibly three jacks with one ofthem mounted centrally to facilitate control and avoid a hyperstaticarrangement. These jacks are fitted with attachment means permitting asemi-pendular suspension of the silo/metering device assembly, in orderto reduce stresses associated with the movements and to avoid theeffects of possible deformations of the chassis. These means will beformed, for example, by a strap attachment between the axis of the jackand the silo, and attachment by trunnions between the body of the jackand the chassis. If necessary, these trunnions will be equipped to forma universal joint.

The silo 105 is attached to the frame 103 in this way in a sturdy andflexible manner, always being able to carry out vertical translationmovements on command, with respect to said frame, which allows theheight of the spreading of the product with respect to the ground to beadjusted, to influence in particular the level of dust emission.

Furthermore, by actuating the jacks in a differential manner the silowill be able to be tilted to the front or to the rear, which allows theinclination of the hopper, and thus the feed conditions of the meteringdevice, to be varied, to change the flow conditions of the product to bespread. As described later, this variation in inclination also allowsthe silo to be divided into two parts to increase the feed gradients byabout 15°, from approximately 55° to approximately 77°, for example, inorder to improve the feed for the metering device by gravity, withminimum pulverization of the material to be spread.

In the lowest position, the silo will rest on the frame 103, which willprovide a rest position, useful for example for transporting the machineon a trailer. By way of a variant, measuring means, for example straingauges, can be placed at the supports at the end of the travel of thesilo on the frame, which allow the weight of the silo and its contentsto be determined, for example in order to limit filling of the silowhere particularly heavy material is used, and to know the mass spreadbetween two weighing operations.

The inclination of the silo to the front and to the rear, obtained bydifferential action on the jacks, is shown in FIGS. 3 to 5, which alsoshow a variant of the invention where the silo is divided into two partsby a fixed, central, transverse internal partition 201. It can be seenthat the slight inclination of the walls of the high part of the silo,referred to above, allows said silo to be tilted to a maximum extentforwards or backwards without theses walls interfering with the cab 101or the engine 102.

Closing means 204, formed for example by movable flaps, prevent, atwill, the product to be spread from falling into the metering device106. This closure can be made independently for the front part of thesilo and for the rear part. The silo can be completely closed in thisway when it is horizontal, as shown in FIG. 3.

In order to spread the product contained in the front part of the silo,the silo is inclined to the rear, as shown in FIG. 4. The flaps whichseal off this front part are then opened, while keeping closed thosewhich seal off the rear part, and the drum of the metering device isrotated. The product thus falls onto the metering device in the mostvertical manner, since the front partition of the hopper is clearly morevertical than in the position shown in FIG. 3, and the central partition201 has more or less the same inclination.

In this way, under the effect of gravity, a movement towards themetering device of all the mass of the product contained in the frontpart is obtained, and any vaulting or chimney effect which would causepulverization of the product and lead to local variations in thedensity, adversely affecting the uniformity of the spreading operation,is avoided.

When the front part of the silo is empty, the front flaps are closed,the silo is tilted forward and the rear flaps are opened, as shown inFIG. 5, This allows the rear part of the silo to be emptied under thesame conditions as the front part.

More complete use of the volume of the product contained in the silo canalso be obtained in this manner.

When the spreading operation is carried out on a surface by means ofsuccessive strips corresponding to to-and-fro movements of the spreader,one of the parts of the silo can also be used for one strip and theother part for the other strip. In this way, the volume of the productcan be left to stand in each part during half the operating time, whichcontributes to the stabilization of the product.

It is also possible to fill the two parts of the silo with differenttreatment products and to use one or the other as required.

In order to be able to mix products in different and specifiedproportions, possibly variable, for example one part lime to six partscement, where the soil is slightly clayey and not very moist, theinvention proposes to use two separate metering devices of differentsizes, each fed by one part of the silo which is a different size fromthe other part, as shown in FIG. 6. For this, the central partition 201will preferably be moveable so as to tilt about a transverse clevis pin202 situated at the joint 108. The roof of the silo will be arranged toform a hump 203 which, among other things, enables the forward andbackward movement of the partition to modify the volume of these twoparts.

As shown in the figure, the single metering device 106 has been replacedby two rotary metering devices 616 and 626 in parallel and of the samewidth. This replacement is facilitated by the bolt fixing at the joint108. On the other hand, these metering devices have different diametersin relation to the proportions of the products to be spread. Thisrelationship is not necessarily a direct proportion which could lead tovery large differences in diameter, one of the metering devices beingmuch too large and the other much too small. To rectify this drawback,metering devices of reasonably different diameters will then be used andthe desired dosing obtained by rotating them at different speeds ofrotation, the largest rotating faster than the smallest. Conversely, thesmallest will be rotated faster than the largest to reduce the dosingdifference and to be able to use the same set of different meteringdevices without multiplying the number in relation to the desiredvariations in dosing.

When the spreader is to be equipped with such an arrangement, the twoparts of the silo will be filled with quantities of products to bespread which directly correspond to the proportion of the mixture to beobtained, to avoid interruption to the work by reloading one part of thesilo while the other is still not empty. Thus, to be able to completelyrefill the silo, the central partition 201 will be inclined to obtainvolumes from the two parts corresponding to the quantities required. Inpractice, the displacement of this partition will be blocked at thevalue required by a cable of a length determined for this purpose. Thusby filling the part at the side where the cable is situated, thepartition will tilt under the effect of the thrust of the product, untilthe cable is tightened. After this part is filled, the other will thenbe filled, and the spreader will therefore contain the desiredquantities of product.

This arrangement thus allows the formulas of the spread products to beoptimized, for example, in addition to the case already mentioned, bycombining a road binder with cement, or by mixing a pozzolanic flue dustwith a dope.

It is known, furthermore, that the inventor has proposed in Frenchpatent number 2359452 filed on Jul. 21, 1976 under number 7622201 andgranted on Oct. 3, 1980, a spreader with dosing by weight equipped withrecording and monitoring means which enable the quantity of productspread on the soil to be known.

In order to better assess the effectiveness of the soil treatment means,the French Government has developed a measurement method which enables,with a certain degree of approximation, the mean value and the standarddeviation of the distribution of the spreading operation to be known.

This measurement method uses, among other things, canvas to determinethe transverse and longitudinal dispersions, and a measurement of theaxle loads before and after spreading, with the aid of moveable balancesto determine the mean value of this spreading operation.

In order to convert the known result into a direct improvement in thecharacteristics of the spreading operation the invention proposes tocorrect in real time the flow of the product to be spread by influencingthe flow rate of the metering device 106 in relation to this flow ratemeasurement, obtained indirectly by measuring variations in the weightof the silo/silo/metering device assembly 105-106, which gives theweight of spread product.

The weight of this assembly can be measured in different ways. One ofthese consists in placing strain gauges at suitable locations on theattachment points of the silo 105 on the frame 103. The other wayconsists in measuring the oil pressure in the hydraulic system foradjusting the height of the silo. This second way is simpler, but itrequires this height to be effectively adjusted by a hydraulic system.

A measurement of the variation of this weight is obtained from theinstantaneous weight measurement by controlled electronic means, andthus the dose spread per unit of area is directly determined bymeasuring the speed of advance of the spreader. The speed of rotation ofthe drum of the metering device 106 can then be adjusted to continuouslymaintain this value at the chosen desired value by means of a system ofautomatic regulation. The performance of electronic systems currentlyavailable enable this regulation to be obtained with a margin of errorwhich is completely satisfactory for the known requirements.

Furthermore, by known methods of fine analysis of the variations of thesignals thus obtained, the variations in the slip of the product in thesilo leading to overloading or discharging of the metering device, forexample, can be accurately determined. Knowledge of these movements willthen enable corrective action to be implemented, for example bydisplacing the silo forwards or backwards to regularize the distributionof the material in the silo. If required, recording these signals over asufficiently long period will allow corrective action to be taken on thestructure of the silo, for example by modifying the shape andinclination of the partitions, or inserting moveable internal partitionsat locations which depend on the materials employed.

The simple solution for managing this system consists in using asuitably programmed PC-type microcomputer. The functions to becontrolled being relatively simple, a considerable treatment capacitywill thus be available, which can be used for functions which aresupplementary to the invention.

The invention therefore further proposes to use sensors connected tothis electronic device to identify the line of demarcation between thesection of soil which has received the treatment product and the sectionof this soil which has not received it. These sensors can operate indifferent ways, by detecting contrast, temperature or height difference,etc. Having obtained this information in this manner, it is easy toprocess it to determine corrective action enabling the trajectory of thespreader to be corrected in order to adjust the connection between thestrips of treated soil. This can be done either by signals to the driveror even by automatic action on the steering of the towing vehicle.

The invention also proposes to place safety sensors which allow theoperation of the spreader to be interrupted at any time when specificparameters linked to the discharge cycle or to safety, such as thepresence of obstacles, or excessive tensile stress on the shearingdevices or mixing of the soil, are exceeded.

As was seen above, an important dust source is that due to the fillingof the hopper, especially when this filling is carried out with pulsedair.

In order to eliminate these drawbacks, the invention therefore proposesto use an industrial filter of a known type, shown only in a rear viewin FIG. 7, and in a side view and coupled to the spreader according tothe invention, in FIGS. 8 and 9.

This filter 701, of the diaphragm type for example, is connected to afilter cyclone 702 and is driven by a compressor unit 703. The assemblyis placed on a trailer 704.

Advantage is taken of the small space taken by the length of thespreader while transporting the assembly between two sites by couplingthe trailer onto the spreader, as closely as possible to said spreader,as shown in FIG. 9. This enables this assembly to be transported on asingle vehicle, of the cart type for example, and to thus economize ontransportation means.

Similarly, for movements within the site, this small space requirementenables the filter to be towed by connecting the trailer to the spreaderby a drawbar 705, as shown in FIG. 8; the spreader acting as the towingvehicle. There is therefore no need to make the filter self-propelled orto provide a separate towing vehicle.

On the site, the trailer is unhitched to park it at the area where theproducts to be spread are dumped. During the spreader loading operationsthe silo 105 of the spreader is connected to the filter cyclone 702 by aflexible hose, not shown, which is connected to an opening 706. Thepulsed air having been used for the transfer of the product into thesilo is then filtered in this assembly and escapes cleanly into theatmosphere by the opening 707. Compressed air contained in a reservoir708, for example, can be used to blow out and purge the assembly of thedust thus accumulated, and to return it to the storage silo.

It is known in the prior art that, having spread the product on thesoil, it is then mixed with the earth by mixing the soil and the productwith the aid of a device such as, for example, a cutter carried on avehicle operating independently. Besides the additional dust sourceresulting from this mixing operation, the presence of the loose producton the soil during an unspecified time between two operations, stillcauses an additional risk of direct action of wind on this productlayer, which is extremely sensitive to the action of the wind when it isin a relatively thin layer on the soil. Apart from this nuisance causedby the wind, quality problems of a meteorological origin due to theaction of rain, which can wash off the product layer prior to mixing,can also arise.

Now the thermal output of the engine 102 is specified to allow themovement of the spreader in difficult conditions, notably at full load,at high speed, on difficult ground having poor lift, on ramps with steepgradients, etc.

During the spreading operations, which generally take place onwell-prepared and flat ground and at a moderate speed, a considerablespeed reserve is therefore available, all the more so since the means ofthe invention demand only a small amount of power for the actualspreading itself, because of the extraction of the product by gravityand the use of a rotary metering device.

It should furthermore be noted that the prismatic shape of the lowerpart of the silo of the spreader makes available, according to theinvention, at the front and at the rear of the spreader, a large freespace which enables various supplementary means to be housed, which areshown in FIGS. 10 and 11, respectively, in two end positions, one anoperating position and the other a completely raised position fortransfer of the spreader outside the spreading operations.

The invention therefore proposes to combine at least the two spreadingand mixing operations, or at the very least premixing operations, in asingle operation by placing mixing means on the spreader, such as atleast one cutter 112 situated just to the rear of the metering device106. This cutter is connected to the rest of the machine by adjustableattachment means such as the arms 118, which are advantageouslyarticulated onto the chassis to be supported by this chassis, which willbear the reaction forces.

This cutter is indirectly driven by the engine 102 via a hydraulictransmission system. It is driven by a relatively slow movement and itprovides mixing of the soil with the material to be spread with maximumprevention of the formation of dust. Furthermore, a casing (or bell) 109to cover the cutter can be advantageously used, which will be capable ofpartially covering the casing of the metering device without touchingit, to prevent mutual interference between these casings.

The slow premixing movement obtained in this way enables the powderyproduct to be introduced into the soil and to be covered with earth.When the mixing subsequently takes place after the passing of thespreader at the time of the action of the powerful cutter of a mixerwhich is intended to energetically mix the soil and the product, theteeth of the rotor no longer directly act on the product deposited onthe surface of the soil. The level of dust emission is thereforeconsiderably reduced.

The fact of proceeding with premixing of the binding agent with the soilafter spreading means that the rear wheels of the spreader no longercrush the section of binding agent as described above, but thesoil/binding agent mixture.

Since the mixing width is greater than the external width betweenwheels, the passing of the wheels causes a vertical deformation bycompaction in the uncompacted soil due to the imprint of the wheel,without causing lateral movements.

It follows that the spacing between the rear wheels no longer representsa design constraint for the spreader. In particular, the wheels can beas far apart as possible so as to increase the stability of the machine.

The width of the spreading operation is therefore freely determined, theonly requirement being to proceed with mixing which is wider than thewidth of the spreading operation and to include the width of the wheelsto some extent so as to obtain a lateral stop and to avoid collapse ofthe soil/binding agent wall with displacement as the wheel passes by.

This solution is of interest in producing low capacity spreaders,capable of being adapted to use on small sites. It also enables fixedaxles whose wheels are possibly guiding wheels, to be used instead ofwheels pivoting through 180°.

Thus to prevent mixing between the part having received binding agentand that which has not received it, the mixing chamber will bepartitioned by a disc similar to that of a plough inserted in the cutterat the limit of the spreading area. Moreover, any interference betweenthe strips is avoided in this way and the part which has received thebinding agent is perfectly delimited.

The repeat operation will then be carried out by juxtaposition ofcontiguous strips.

When sites are being developed which do not require premixing, butmixing over the entire width, two small mixers placed in front of eachwheel, respectively, will be advantageously used.

An operating economy will be obtained since the width of the mixing isreduced.

The width of each cutter will be determined with respect to thesoil--soil/binding agent demarcation line, with a border related to theinner mould of the tyre of the wheel, to avoid collapse, and, for thesame reason, a border related to the external demarcation line, withoutthe border corresponding exactly to the width of the tyre.

The installation and the mechanical drive of these two cutters can berealized with the aid of devices and an axle which are common to both.

Taking into account the available space at the front of the spreader,and the desirable limits of the mixing forces at the cutter situated atthe rear of the spreader, the invention also proposes to prepare thesoil in advance of the spreading of the product, so that the mixingmeans 112 can act on the soil which has already been prepared, that isloosen, so as to facilitate the mixing operation while reducing theforces at this level and thus minimizing to a maximum extent thecreation of dust.

For this, soil shearing means are used, such as a rotor 111 fitted withpicks and placed under a casing 113 which hides it in the figure wherethe rotor is denoted by its spindle. This casing (or bell) 113 willenable any production of dust to be limited, which can be produced, forexample, in the case of very dry soil. The rotor is attached to theframe 103 by arms 110 which allow it to be raised when not in use, andto lower it to sink it more or less into the soil, depending on therequirements. Openings 114 made in the lateral walls of the casing 113allow it to rest on the soil at all times, whatever the depth of therotor.

By lowering the rotor fitted with picks into the soil by ten or socentimeters, for example, these picks then shear the soil and aerate itso that it emerges in the form of a loose layer 115 behind said picks,to receive the product delivered by the metering device 106. It is thenmixed by the cutter 112 and forms a treated layer 116.

The use of such a device driven by a movement obtained by means of amotor, hydraulic for example, allows the tensile stress exerted on therotor by the frame to be minimized. The power required for the shearingof the soil will therefore be basically transmitted from the main motorby hydraulic transmission. The total power will certainly be supplied bythis motor, which also drives the tractor part, but the force at thewheels will be minimized, which can be large depending on the state ofthe soil and the dimensions of the driving wheels.

The heights in relation to the soil of each of these pieces ofequipment, whether they be the metering device 106, the cutter 112 orthe ripper rotor 111, can be adjusted separately so as to optimize theoperating conditions of the assembly, perhaps even in such a way thatonly one of them is used in particular cases.

FIGS. 12 and 13 show a variant of the spreader shown in FIGS. 10 and 11,in which none of the ripping means described above are used.

The cutter is contained in a casing 309 which always rests on the soilin operation, thanks to an opening 314 which allows verticaldisplacement of the cutter spindle. The metering device 106 itself isenclosed in a casing 319 which in operation also rests on the soil atall times. The casing 319 contains a longitudinal rear opening 301, andthe casing 309 has a longitudinal front opening 311 to allow the layerof spread product to pass without hindrance. These openings are providedto allow the two casings to fit one within the other when they arelowered into the operating position, thus ensuring very good sealingaround the metering device and the cutter.

In this version, the lower opening of the hopper can be moved forwardwhile increasing the available space at the rear of the spreader. Thisallows the dimensions, and thus the power and the size, of the cutter tobe increased and to obtain a machine in which the two functions ofspreading and complete mixing to a great depth are combined. Besides thesolution of the dust problems, the use of two separate machines whichoperate in two successive passes is thus avoided. The economy producedby this means is obvious and is especially useful in short-termoperations. Furthermore, on a large-scale site where conventional typespreaders are already present, if need be, the spreader according to theinvention can be used exclusively for mixing by not lowering the cutterand keeping the other devices raised.

In this spreader, shown in FIG. 14, a large, high-powered cutter 312 isused, which enables direct, complete and definitive mixing to be carriedout without running an additional machine.

Mixing at high speed can thus be obtained in one pass, therefore savingconsiderable time in the execution of the work, without increasing thenuisance due to dust.

While the spreader according to the invention is described in relationto a self-propelled platform, the invention extends to other types ofvehicles which are generally used for spreading, for exampleself-propelled towing vehicles and towing vehicles with trailer.

I claim:
 1. A spreader for treating soil with a treatment productcomprising a silo having a lower part forming a hopper, said hopperbeing in the form of a truncated prism having an upper base and a lowertruncated part, a metering device attached to said lower part, saidlower part and said metering device extending substantially over theentire width of the spreader to treat the soil over substantially theentire width of the spreader without trituring the product to be spread,a frame open over substantially the entire width of the spreader forreceiving the silo, and supporting devices for effecting translatorymovement of the silo and the metering device including raising andlowering the silo and the metering device vertically relative to thesoil to adjust the elevation of the metering device above the soil to betreated.
 2. A spreader according to claim 1 wherein said supportingdevices are mounted on said spreader for tilting the silo and themetering device forwards and backwards relative to a transverse axis. 3.A spreader according to claim 1 wherein said supporting devices compriseextensible and retractable jacks disposed adjacent the periphery of thesilo and having articulated connections with said silo.
 4. A spreaderaccording to claim 1 wherein said metering device comprises a largediameter rotor having small cells.
 5. A spreader according to claim 1including means for releasably attaching said metering device to thehopper, enabling replacement thereof by a different type of meteringdevice.
 6. A spreader according to claim 1 wherein said frame has atransverse cross-section constant with respect to the longitudinal axisof the spreader and said silo has a width substantially correspondingwith respect to the width of the opening of the frame.
 7. A spreaderaccording to claim 6 including four wheels pivotable through 180° anddisposed at the four corners of said frame to widen the track, increasestability of the spreader and avoid crushing edges of the strips ofmaterial discharged onto the soil.
 8. A spreader according to claim 1including a generally vertical, transversely extending, centralpartition dividing the silo into two parts, and a closure for controlledclosing of the junction between said parts and the metering device toenable feed from one or another of said two parts of the silo.
 9. Aspreader according to claim 8 including two rotatable metering devicesof different diameters for feeding product from each of the two parts ofthe silo respectively, said vertical central partition being movable todelimit two unequal parts whose volumes correspond to the flow rates ofthe metering devices.
 10. A spreader according to claim 1 including afilter supported by a trailer and coupled to the spreader in atransportation position, said silo having an opening for connection withsaid filter enabling air within the silo to be evacuated.
 11. A spreaderaccording to claim 1 including a mixing means disposed behind saidmetering device to mix the soil and product spread on the soil, andmeans for attaching said mixing means to the frame enabling adjustmentof the height of said mixing means with respect to the soil.
 12. Aspreader according to claim 11 including two casings enclosing themixing means and the metering device, respectively, and containingopenings fitted together one within the other in the operating positionto seal the assembly thereof.
 13. A spreader according to claim 11wherein said mixing means are divided into two separate parts withrespect to a longitudinal plane of symmetry through the spreader anddisposed in front of each of the rear wheels, respectively, forming anon-mixing space therebetween to mix two strips of soil for crushing bysaid rear wheels.
 14. A spreader according to claim 11 including soilshearing means disposed in front of said metering device to loosen thesoil prior to spreading the product, and means for attaching saidshearing means to said frame and for adjusting the height thereof withrespect to the soil, said attaching means being operable independentlyof said extensible and retractable devices.
 15. A spreader according toclaim 14 wherein said shearing means are fitted with an independentmotor enabling the tensile stress of the spreader on the shearing meansto be minimized.
 16. A spreader according to claim 1 including means formeasuring the weight of the silo and the metering device, means forprocessing signals obtained by said measuring means to determine fromthe variation in the measured weight the flow of the product spread onthe soil and to control the flow rate of the metering device to obtain auniform distribution of the product on the soil.
 17. A spreaderaccording to claim 16 wherein said supporting devices include extensibleand retractable devices, said measuring means operating on oil pressurein said extensible and retractable devices.
 18. A spreader according toclaim 1 including means enabling the position of the strip of productspread on the soil to be detected and the direction of advance of thespreader to be controlled to maintain the successive strips of spreadproduct contiguous with each other.